Laser range finder

Abstract

A method and an apparatus for measuring the distance to a target according to the time-of-flight of laser pulses. The apparatus includes a transmitter of laser impulses toward the target and a receiver of laser impulses reflected from the target. A driver of the transmitter generates a first time signal corresponding to the transmission. The receiver generates a second time signal corresponding to the reception. A delay generator delays at least one of the first and second signals to compensate for time errors, and provides a third signal corresponding to the first signal and a fourth signal corresponding to the second signal, such that a time difference between the third and fourth signals is exactly equal to the time-of-flight of the transmitted pulses. Additional circuitry delays the earlier of the third and fourth signals so as to provide signals that are delayed by incrementally increasing amounts of time relative to the earlier signal, and matches a time the later signal of the third and fourth signals to one of the incrementally delayed signals, thereby to obtain a time delay value approximating the time-of-flight. In a preferred embodiment, the delay generators are digitally programmable and are controlled by a microprocessor to find the match to the later of the third and fourth signals by using a binary search procedure.

What is claimed is: 
     
       1. A method of measuring the distance between a target and a ranging apparatus based on time-of-flight of laser impulses, comprising the steps of: transmitting laser impulses from the apparatus toward the target and generating a first time signal corresponding to the transmission;   receiving with the apparatus, laser impulses reflected from the target and generating a second time signal corresponding to the reception;   delaying at least one of the first and second signals to compensate for time errors so as to provide a third signal corresponding to the first signal and a fourth signal corresponding to the second signal, a time difference between the third and fourth signals being exactly equal to the time-of-flight of the transmitted pulses;   delaying the earlier of the third and fourth signals so as to provide a plurality of fifth signals, the fifth signals delayed by incrementally increasing amounts of time relative to the earlier of the third and fourth signals; and   matching the time of the later of the third and fourth signals to the time of one of the fifth signals, to obtain a time delay value approximating the time-of-flight.   
     
     
       2. The method of claim 1, wherein said step of matching includes a binary search. 
     
     
       3. A ranging apparatus for measuring the distance of a target and the apparatus based on the time-of-flight of laser impulses, comprising: means for transmitting laser impulses toward the target and generating a first time signal corresponding to the transmission;   means for receiving laser impulses reflected from the target and generating a second time signal corresponding to the reception;   delaying means for delaying at least one of the first and second signals to compensate for time errors so as to provide a third signal corresponding to the first signal and a fourth signal corresponding to the second signal, a time difference between the third and fourth signals being exactly equal to the time-of-flight of the transmitted pulses; and   delaying and matching means for delaying the earlier of the third and fourth signals so as to provide a plurality of fifth signals, the fifth signals delayed by incrementally increasing amounts of time relative to the earlier of the third and fourth signals, and for matching the time of the later of the third and fourth signals to the time of one of the fifth signals, to obtain a time delay value approximating the time-of-flight.   
     
     
       4. The apparatus of claim 3, wherein said first and second delaying means comprise digitally programmable delay generators. 
     
     
       5. The apparatus of claim 3, wherein said delaying and matching means includes at least one digitally programmable delay generator and a microprocessor for controlling said at least one digitally programmable delay generator. 
     
     
       6. The apparatus of claim 3, wherein at least one digitally programmable delay generator comprises at least two serially connected, digitally programmable delay generators. 
     
     
       7. A ranging apparatus for measuring the distance of a target from the apparatus based on the time-of-flight of laser impulses, comprising: means for transmitting laser impulses toward the target and generating a first time signal corresponding to the transmission;   means for receiving laser impulses reflected from the target and generating a second time signal corresponding to the reception;   a processing unit, including first delaying means including at least a first digitally programmable delay generator, for delaying at least one of the first and second signals to compensate for time errors so as to provide a third signal corresponding to the first signal and a fourth signal corresponding to the second signal, a time difference between the third and fourth signals being exactly equal to the time-of-flight of the transmitted pulses,   second delaying means, including at least a second digitally programmable delay generator, for delaying the earlier of the third and fourth signals so as to provide a plurality of fifth signals, the fifth signals delayed by incrementally increasing amounts of time relative to the earlier of the third and fourth signals, and     a D-type flip-flop connected to receive in separate ports the fifth signals and the later of the third and fourth signals; and   a microprocessor, monitoring the output of said D-type flip-flop, and controlling said second digitally programmable delay generator, to perform a binary search so as to match the time of the later of the third and fourth signals to the time of one of the fifth signals, thereby to obtain a time delay value approximating the time-of-flight.